The goals of this grant are two-fold: The first is to establish funding for the principle investigator to secure a faculty position and develop an independent research program. The second goal is to further characterize the interaction of bacteria and their products with intestinal epithelial host cells. Specifically, experiments are proposed to identify specific regions of pathogenic bacterial flagellin that induce proinflammatory responses and establish how these regions are translocated across polarized epithelial cells to allow recognition of toll- like receptor 5 (TLR5) localized on the basolateral surface. Gram-negative bacterial shock is mediated by the actions of proinflammatory genes induced in response to microbes and their products. Among the surface components of Gram-negative bacteria, a protein that is released by Salmonella, and other pathogenic bacteria, known as flagellin has been shown to potently induce a variety of proinflammatory responses in a number of mammalian cells. Flagellin, the primary structural component of flagella, from Salmonella species and other flagellated bacteria has highly conserved amino and carboxyl termini and a hypervariable central region. The host response to flagellin is being elucidated but additional work is necessary. The conserved regions of flagellin have been shown to induce a vigorous inflammatory response such as lL-8 secretion and nitric oxide production in intestinal epithelial cells via the IkBa/NF-kB pathway. This inflammatory response to flagellin appears to be mediated by TLR5 located on the basolateral surface of intestinal epithelial cells. The data indicates that flagellin plays a crucial role in upregulating inflammation during bacterial infection of the host and is primary microbial factor recognized by the TLR5. The specific aims of this proposal are: 1) to establish the minimal proinflammatory domain(s) within the conserved termini of Salmonella dublin, as well as other pathogenic bacterial flagellin proteins and determine if these same region(s) mediate TLR5 binding, and 2) to determine the mechanism by which live Salmonella mediate the translocation of flagellin across intestinal epithelial cells inducing inflammatory responses in contrast to nonpathogenic intestinal bacterial flora. These studies will provide insights into bacterial and host cells interactions that are critical for establishing disease and will offer new avenues for the development of treatment.